Stent delivery systems for deploying stents are a highly developed and well known field of medical technology. Stents have many well known uses and applications. A stent is a prosthesis which is generally tubular and which is expanded radially in a vessel or lumen to maintain its patency. Stents are widely used in body vessels, body canals, ducts or other body lumens.
The delivery systems for stents are generally comprised of catheters with the stent axially surrounding the distal end of the catheter. It is highly desirable to keep the profile of the catheter as small as possible. Therefore, self-expanding stents are generally confined in a reduced radius for delivery to the deployment site. Once the stent is deployed the catheter is removed, leaving the stent implanted at the desired location to keep the vessel walls from closing.
A variety of techniques have been developed for holding a self-expanding stent in its reduced configuration while moving the distal end of the catheter to the deployment site. For example, in U.S. Pat. No. 4,655,771 to Wallsten, gripping members at either end of the stent hold the stent in an axially-elongated position, which causes the stent to take a reduced radius delivery configuration.
Another common technique for maintaining the self-expanding stent in a reduced radius delivery configuration is using a sheath which surrounds the stent and compresses it around the catheter. This technique is disclosed in U.S. Pat. No. 5,071,407 to Termin and U.S. Pat. No. 5,064,435 to Porter, both of which use a silicon rubber sheath to compress the stent. A similar technique is disclosed in U.S. Pat. No. 5,026,377 to Burton and U.S. Pat. No 5,078,720 to Burton.
Unfortunately, deployment of stents, in particular, long and/or large stents, which are held in place by sheaths applying high frictional forces and compressive forces, can be quite difficult. Use of a manually operated pull-wire is not always adequate to retract a sheath. It is therefore desirable to provide a means for retracting sheaths which can apply sufficient force to overcome these high forces.
To that end, a catheter employing a piston-based hydraulic sheath retraction mechanism has been disclosed in co-pending, commonly assigned U.S. patent application Ser. No. 08/633,726, the entire contents of which are incorporated herein in its entirety by reference. Further to that end, the present invention provides a medical device delivery apparatus which employs a piston-based hydraulically operated retraction mechanism to apply sufficient force to the retractable sheath so as to withdraw the sheath from its initial position over the stent. The present invention also provides methods of delivering a medical device using a medical device delivery apparatus comprising a hydraulically operated piston.